Apparatus for assembling a stator core

ABSTRACT

An apparatus for assembling a stator core having a plurality of radially disposed and radially movably jigs for holding the segmented cores. Vertically movable cams are provided vertically downwards on an upper vertically movable plate. By lowering the movably plate, the jigs are pushed radially inwards, thereby causing the plurality of segmented cores circumferentially to approach each other. The projection of each segmented core is fit by press fitting into the groove of the adjoining segmented core in the circumferential direction, thereby connecting the segmented cores together.

This application is a divisional of prior application Ser. No.09/078,683, filed on May 14, 1998 now U.S. Pat. No. 6,219,900; which isa divisional application of prior application Ser. No. 08/803,228, filedon Feb. 20, 1997, which issued as U.S. Pat. No. 5,786,651.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a stator core which is used in a rotaryelectric machine such as an electric motor or the like. It also relatesto a method of assembling the stator core as well as to that apparatusfor assembling the stator core which is used in carrying out the method.

2. Description of the Related Art

As can be seen in the Japanese Published Unexamined Patent ApplicationNo. 124241/1986, there is conventionally known the following statorcore. Namely, a segmented (or divided) core is made up of an arcuateyoke portion, a pole portion which extends diametrically inwards fromthe yoke portion, and a tooth portion on a diametrically inner end ofthe pole portion. On one circumferential end and on the othercircumferential end of the yoke potion, there are formed a projectionand a concave groove (hereinafter simply called a groove), respectively.A plurality of segmented cores each being formed as described above arecircumferentially connected together (i.e., connected together in thecircumferential direction) such that a projection of one of adjoiningsegmented cores is fit into a groove of the other of the adjoiningsegmented cores, thereby assembling a stator core. other of theadjoining segmented cores, thereby assembling a stator core.

In the above-described conventional stator core, the groove is formedinto a dovetail groove and the projection which is formed into adovetail shape is fit by pressing into the groove in an axial directionof the stator core.

Since the stator core is relatively large in its axial length, in theabove-described conventional one in which the projection is fit into thegroove in the axial direction, the stroke of press fitting becomes long.In order to prevent the load of press fitting from becoming excessive,the interference between the projection and the groove must be madesmall. As a result, the segmented cores are likely to give riseexcessive play or are likely to cause rattling among them.

The present invention has a first object of providing a stator core inwhich this kind of disadvantage has been eliminated.

Further, in the above-described conventional stator core, the work ofsubjecting the segmented cores to press fitting in the axial directionmust be carried out in sequence one at a time. It has therefore adisadvantage in that the stator core takes much time to assemble.

In view of the above-described disadvantage, the present invention has asecond object of providing a method of assembling the stator core with agood working efficiency as well as of providing an apparatus forassembling a stator core which is used in carrying out this method.

SUMMARY OF THE INVENTION

In order to attain the above-described first object, the presentinvention is a stator core having a plurality of circumferentiallysegmented cores, each of the segmented cores having a projection and agroove on circumferential one end and the other end, respectively, of ayoke portion thereof. The segmented cores are assembled to form a statorcore by circumferentially connecting the plurality of segmented cores byfitting a projection in one of adjoining segmented cores into a groovein the other of the adjoining segmented cores. The stator core ischaracterized in that: a straight portion is formed in an intermediateportion of each of the projection and the groove, the straight portionextending straight in a predetermined width in a normal direction whichis normal to each end surface of the yoke portion; that a front endportion of the projection and an inner bottom portion of the groove areformed into a semicircular shape having a diameter equal to a width ofthe straight portion; and that a contracted portion which adjoins thestraight portion and has a width smaller than the width of the straightportion, and an enlarged width portion which extends in width from thecontracted portion towards each end surface of the yoke portion areformed in those portions of the projection and the groove which arerespectively closer to each end surface of the yoke portion; such that,when the projection is fit by press fitting into the groove in thenormal direction, the contracted portion of the groove is enlarged inwidth within an elastic region of groove walls on diametrically outerside and inner side, respectively, of the groove to thereby allow thestraight portion of the projection to pass therethrough and, that oncethe straight portion of the projection has passed through the contractedportion of the groove, the straight portion and the contracted portionof the groove are brought into forced contact with the straight portionand the contracted portion of the projection, respectively.

According to the above-described arrangement, it becomes possible to fitby press fitting the projection of one of circumferentially adjoiningsegmented cores into the groove of the other of the adjoining segmentedcores in the normal direction which is normal to the end surface of theyoke portion, i.e., in the circumferential direction. Therefore, thestroke of the press fitting becomes extremely shorter than the one inwhich the projection is fit by press fitting in the axial direction. Asa result, even if a relatively large interference between the projectionand the groove is maintained, the load of press fitting will not becomeexcessive. Further, due to the presence of the straight portions, thetilting of the segmented cores with the fit portion of the projectionand the groove functioning as a fulcrum can be prevented. In conjunctionwith the fact that the interference can be sufficiently secured, therattling of the segmented cores can surely be prevented. Therefore, astator core of high quality can be obtained.

If the groove is formed such that the widthwise center line of thestraight portion coincides with the normal line that passes through thewidthwise center of the end surface of the other end of the yokeportion, the groove wall on the diametrically outer side of the groovebecomes thinner than the groove wall on the diametrically inner side ofthe groove. As a result, the bending rigidity of the groove wall on thediametrically outer side of the groove becomes smaller than the bendingrigidity of the groove wall on the diametrically inner side of thegroove. Therefore, when the projection is fit by press fitting into thegroove, only the groove wall on the diametrically outer side isdeflected, and there will occur a step (or a stepped surface) in thediametrical direction between the adjoining segmented cores.

Therefore, it is preferable to form the groove in a manner that awidthwise center line of the straight portion is offset diametricallyinwards relative to the normal line passing through the widthwise centerof the end surface of the other end of the yoke portion such that thebending rigidity of the groove wall on diametrically outer side of thegroove becomes equal to the bending rigidity of the groove wall ondiametrically inner side thereof.

Further, if the length of the straight portion of the projection is madeslightly longer than the length of the straight portion of the groove tosecure an interference in the normal direction between the contractedportions of the projection and the groove, the play among the segmentedcores in the circumferential direction can advantageously be removedcompletely.

In order to attain the above-described second object, the presentinvention is a method of assembling a stator core which has a pluralityof segmented cores. Each of the segmented cores has an arcuate yokeportion, a pole portion extending diametrically inwards from the yokeportion, and a tooth portion on a diametrically inner end of the poleportion. The yoke portion has a projection and a groove oncircumferential one end and the other end, respectively, thereof. Thesegmented cores are assembled to form a stator core by circumferentiallyconnecting the segmented cores by fitting a projection in one ofadjoining segmented cores into a groove in the other of the adjoiningsegmented cores. The method comprises the steps of: arranging theprojection circumferentially insertable into the groove; disposing theplurality of segmented cores into an annular shape; and then pushing theplurality of segmented cores radially inwards in a manner synchronizedwith each other; such that the projection in each of the segmented coresis fit by press fitting into each of the grooves in the adjoiningsegmented cores in a circumferential direction.

Further, an apparatus for carrying out the above-described methodcomprises: a bed; a movable plate which is provided above the bed so asto be movable up and down; a plurality of jigs which hold the segmentedcores and are radially disposed on the bed so as to be radially movable;and cam means which is disposed under the movable plate so as to pushthe plurality of jigs radially inwards simultaneously with a downwardmovement of the movable plate.

In this case, preferably each of the jigs has a recessed potion intowhich each of the segmented cores is inserted in position from an upperside, and an engaging groove with which the tooth portion of each of thesegmented cores is engaged for positioning in the circumferentialdirection.

When the movable plate is lowered in a condition in which each of thesegmented cores is set in position on each of the jigs, the plurality ofjigs are pushed radially inwards in a manner synchronized with eachother. The plurality of segmented cores that are held by these jigsapproach each other in the circumferential direction, whereby theprojection of each of the segmented cores is fit by press fitting intothe groove of each of the adjoining segmented cores in thecircumferential direction. In this manner, the stator core can beassembled efficiently by a single operation, resulting in a largelyimproved workability.

Further, if the tooth portion of each of the segmented cores if set inposition by forming the engaging groove in each of the jigs as describedabove, the circumferential clearance between the tooth portions of therespective segmented cores can be accurately controlled. Therefore, theoccurrence of cogging (i.e., an irregularly aligned surface like in acogged joint) due to the dispersion in the clearances can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and the attendant advantages of the presentinvention will become readily apparent by reference to the followingdetailed description when considered in conjunction with theaccompanying drawings wherein:

FIG. 1A is a plan view of one example of a segmented core which is aconstituting unit in assembling a stator core;

FIG. 1B is an enlarged plan view around a projection of the segmentedcore;

FIG. 1C is an enlarged view around a groove of the segmented core;

FIG. 2 is a vertical sectional view of an apparatus for assembling astator core according to the present invention;

FIG. 3 is a cross-sectional view taken along the line III—III in FIG. 2;and

FIG. 4 is a perspective view of a jig which is provided in the apparatusfor assembling the stator core.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

With reference to FIG. 1A, numeral 1 denotes a segmented core which is aconstituting unit (or element) of a stator core. The segmented core ismade by laminating a number of punched pieces which are punched from aband-shaped steel plate.

The segmented core 1 is provided with an arcuate yoke portion 2, a poleportion 3 which extends diametrically inwards from a center of the yokeportion 2, and a tooth portion 4 on a diametrically inner end of thepole portion 3. A stator coil 5 is wound around the pole portion 3 via abobbin 5 a. In order to lie along an end surface of the stator coil 5,the surface on the diametrically inner side of the yoke portion 2 isformed into a flat surface which crosses at right angles to the poleportion 3.

On one circumferential end and the other circumferential end of the yokeportion 2, there are formed a projection 6 and a groove 7, respectively.It is thus so arranged that the projection 6 of each segmented core 1can be fit by press fitting into a groove 7 of each of the adjoiningsegmented cores 1 in a circumferential direction.

As clearly shown in FIGS. 1B and 1C, in each of an intermediate portionof the projection 6 and of the groove 7, there is each formed a straightportion 6 a, 7 a which extends straight, in a predetermined width, in anormal direction which is normal to each end surface of the yoke portion2. Each of the front end portion 6 b of the projection 6 and the innerbottom portion 7 b of the groove 7 is formed into a semicircular shapewhose diameter is the same as the width of the straight portion 6 a, 7a.

In that portion of each of the projection 6 and the groove 7 which iscloser to the end surface of the yoke 2, there are formed: a contractedportion 6 c, 7 c which adjoins (or lies next to) the straight portion 6a, 7 a and is smaller in width than the straight portion 6 a, 7 a; andan expanded width portion 6 d, 7 d which expands in width towards eachend surface of the yoke portion 2. The contracted portion 6 c, 7 ccontinues to a side edge of the straight portion 6 a, 7 a via an arc ofa circle “a” having a diameter that is the same as the width of thestraight portion 6 a, 7 a. The width of the contracted portion 6 c, 7 cis made slightly (e.g., about 0.05 mm) narrower than the width of thestraight portion 6 a, 7 a by the difference between the diameter of thecircle “a” and the length of the chord of the circle “a” that passesthrough the contracted portion 6 a, 7 a.

The enlarged width portion 6 d of the projection 6 and the enlargedwidth portion 7 d of the groove 7 are congruent with each other.However, the width and the length of the straight portion 6 a of theprojection 6 are made slightly larger than the width and the length ofthe straight portion 7 a of the groove 7. For example, in case theradius of the diametrically outer surface of the yoke portion 2 is 79.5mm, and the width T of each end surface of the yoke portion 2 is 9.5 mm,the length L1 of the straight portion 6 a of the projection 6 and thewidth thereof are respectively set to be 1.0 mm and 6.02 mm, and thelength L2 of the straight portion 7 a of the groove 7 and the widththereof are respectively set to be 0.98 mm and 5.98 mm.

Further, since the surface of the diametrically inner side of the yokeportion 2 is formed into a flat surface as described above, the groove 7which recedes from the end surface of the yoke 2 in the normal directionwhich is normal to he end surface gradually departs away from thesurface of the diametrically inner side of the yoke portion 2 to therebyapproach the surface of the diametrically outer side of the yoke portion2. As a result, if the groove 7 is formed such that the widthwise centerline b of the straight portion 7 a thereof coincides with the normalline c that passes through the widthwise center of the end surface ofthe yoke portion 2, the bending rigidity of the groove wall 2 a on thediametrically outer side of the groove 7 becomes weaker than the bendingrigidity of the groove wall 2 b on the diametrically inner side thereof.As a solution, in the present embodiment, the groove 7 is formed suchthat the above-described center line b is slightly offset diametricallyinwards relative to the above-described normal line c. In this manner,the bending rigidity of the groove wall 2 a on the diametrically outerside and the bending rigidity of the groove wall 2 b on thediametrically inner side become equal to each other. In the case of theyoke 2 having the above-described dimensions, if the amountdiametrically inward offset of the center line b relative to the normalline c is set to be about 0.75 mm, the bending rigidities of both thewall grooves 2 a, 2 b become equal to each other. As a matter of course,the projection 6 is also formed such that the center line b of thestraight portion 6 a is offset diametrically inwards relative to thenormal line c that passes through the widthwise center of the endsurface of the yoke portion 2.

According to the above-described arrangement, when the projection 6 ofthe segmented core 1 is fit by press fitting into the groove 7 of acircumferentially adjoining segmented core 1 in the above-describednormal direction, the contracted portion 7 c of the groove 7 is enlargedin width due to a deflection within an elastic region of the groovewalls 2 a, 2 b on the diametrically outer and inner sides to therebyallow for the passage of the straight portion 6 a of the projection 6.Once the straight portion 6 a of the projection 6 has passed through thecontracted portion 7 c of the groove 7, the straight portion 7 a and thecontracted portion 7 c of the groove 7 are brought into a forced (orurged) contact with the straight portion 6 a and the contracted portion6 c of the projection 6, respectively. Then, due to the forcible contactof the projected portions 6 a and 7 a, the tilting movement of thesegmented core 1 with the fit portion of the projection 6 and the groove7 functioning as a fulcrum is prevented. Further, since the length ofthe straight portion 6 a of the projection 6 is made slightly longerthan the length of the straight portion 7 a of the groove 7, theinterference in the above-described normal direction between thecontracted portion 6 c of the projection 6 and the contracted portion 7c of the groove 7 can also be secured. As a result, the play in thecircumferential direction between the segmented cores 1, 1 that adjoinin the circumferential direction can be completely removed. Stillfurthermore, since the bending rigidities of both the groove walls 2 a,2 b on the diametrically outer and inner sides of the groove 7 are madeequal to each other, both the groove walls 2 a, 2 b are evenlydeflected, whereby the projection 6 is correctly fit into the groove 7along the center line thereof. Thus, the segmented cores 1, 1 thatadjoin each other in the circumferential direction can be accuratelyconnected to each other into a condition in which those end surfaces ofthe yoke portions 2, 2 that cross the above-described normal line atright angles are brought into close contact with each other, withoutgiving rise to rattling or a deviation (or a step) in the diametricaldirection.

The stator core is assembled by circumferentially connecting a pluralityof the above-described segmented cores 1 into an annular shape. Theassembling thereof is carried out by employing an apparatus forassembling the stator core (also called an assembly apparatus) as shownin FIGS. 2 and 3.

The assembly apparatus is constituted by an apparatus similar to apressing apparatus. The assembly apparatus is provided with a bed 10 anda movable plate 11 which is moved up and down by a driving source forpressing purpose such as a ram or the like.

On an upper surface of the bed 10, there is mounted a supporting plate12 which is provided with a plurality of radially disposed guide holes12 a. On the supporting plate 12 there are radially disposed a pluralityof jigs 13 which can hold thereon the segmented cores 1. A guideprojection 13 a which is provided on a lower surface of each of the jigs13 is engaged with each of the guide holes 12 a. On the bed 10 there aremounted a central holding plate 14 ₁ and an annular peripheral holdingplate 14 ₂, which prevent the jig 13 from being lifted, via supportingcolumns 14 a, 14 b, respectively. Each of the jigs 13 is thus supportedin a manner radially slidable along each of the guide holes 12 a.

Each of the jigs 13 is provided with a recessed potion 13 b into whichthe segmented core 1 can be inserted for setting in position from anupper side. As shown in FIG. 4, in a radially inner portion of therecessed portion 13 b, there are vertically provided a pair of smallerprojections 13 d, 13 d in a projecting manner with a distance from aninner end rising portion 13 c. This rising portion 13 c and the smallprojections 13 d, 13 d constitute an engaging groove 13 e into which thetooth portion 4 can be engaged by positioning in the circumferentialdirection.

On the lower surface of the movable plate 11, there are provided, in adownwardly projecting manner, cams 15 each having a lower end inclinedcam surface 15 a which can be abutted with an inclined surface 13 f on aradially outer end of each of the jigs 13. Further, there is mounted, onthe lower surface of the movable plate 11, an annular pad 16 whichprevents the segmented cores 1 from being lifted, by abutting with theyoke portions 2 of all the segmented cores 1 from an upper side. Theannular pad 16 is urged downwards by springs 16 a. In this embodiment,the cams 15 are separately provided for respective jigs 13. It may,however, be so arranged that a single piece of annular cam that iscommon to all the jigs 13 is provided.

In assembling the stator core, each of the segmented cores 1 is set inposition on each of the jigs 13 in a condition, as shown in the lefthalf portion of FIG. 2, in which the movable plate 11 is returned to anupper position and in which all the jigs 13 are returned to a radiallyoutward position. In this condition, as shown in the left half portionof FIG. 3, the plurality of segmented cores 1 are arranged into anannular shape in a state in which the front end portion 6 b of theprojection 6 of each of the segmented cores 1 is positioned into (ordisposed inside) the enlarged width portion 7 d of the groove 7 of eachof the segmented cores 1 that adjoin in the circumferential direction.

Then, as shown in the right half portion of FIG. 2, the movable plate 11is lowered. As a result of this operation, all of the jigs 13 are pushedby the cams 15 to thereby advance radially inwards in a mannersynchronized with each other, and the plurality of segmented cores 1that are held on the jigs 13 are brought close to each other in thecircumferential direction. Then, the projection 6 of each of thesegmented cores 1 is fit by press fitting into the groove 7 of each ofthe adjoining segmented cores 1 in the circumferential direction, i.e.,in the normal direction which is normal to the end surface of the yokeportion 2. The plurality of segmented cores 1 are thus connectedtogether in the circumferential direction as shown in the right halfportion of FIG. 3.

In this condition, the straight portion 7 a and the contracted portion 7c of the groove 7 are respectively brought into forced (or urged)contact with the straight portion 6 a and the contracted portion 6 c ofthe projection 6, respectively, with a sufficient interference asdescribed above. The segmented cores 1 are thus connected togetherwithout clattering, and the flatness of the segmented cores 1 is securedby the lifting prevention of the segmented cores 1 by means of the pad16. Further, since the tooth portion 4 of each of the segmented cores 1is positioned in the circumferential direction by means of the engaginggroove 13 e of each of the jigs 13, the clearance between the toothportions 4, 4 of the adjoining segmented cores 1, 1 is maintained to acertain uniform amount. A stator core of high quality can therefore beobtained.

It is readily apparent that the above-described stator core, as well asa method and an apparatus for assembling a stator core meet all of theobjects mentioned above and also has the advantage of wide commercialutility. It should be understood that the specific form of the inventionhereinabove described is intended to be representative only, as certainmodifications within the scope of these teachings will be apparent tothose skilled in the art.

Accordingly, reference should be made to the following claims indetermining the full scope of the invention.

What is claimed is:
 1. An apparatus for assembling a stator core, saidstator core having a plurality of segmented cores, each of saidsegmented cores having an arcuate yoke portion, a pole portion extendingdiametrically inwards from said yoke portion, and a tooth portion on adiametrically inner end of said pole portion, said yoke portion having aprojection and a groove on circumferential one end and the other end,respectively, thereof, said segmented cores being assembled to form astator core by circumferentially connecting said segmented cores byfitting a projection in one of adjoining segmented cores into a groovein the other of said adjoining segmented cores, said apparatuscomprising: a bed; a movable plate which is provided above said bed soas to be movable up and down; a plurality of jigs for holding saidplurality of segmented cores radially disposed on said bed so as to beradially movable; and cam means downwardly provided on a lower surfaceof said movable plate so as to push each of said plurality of jigsradially inwards in synchronization with a downward movement of saidmovable plate, wherein said downward movement of said movable plate isin a direction perpendicular to a direction in which each of said jigsis pushed by said cam means.
 2. An apparatus for assembling a statorcore according to claim 1, wherein each of said jigs has a recessedportion into which each of said segmented cores is capable of beinginserted in position from an upper side, and an engaging groove withwhich said tooth portion of each of said plurality of segmented cores iscapable of being engaged for positioning in the circumferentialdirection.